Oxygen exchange kinetics on solid oxide fuel cell cathode materials-general trends and their mechanistic interpretation

The compilation of measured effective rate constants for oxygen surface exchange on mixed conducting perovskites, which covers a great variety of compositions ranging from (La,Sr)MnO3 - delta to (La,Sr)(Co,Fe)O3 - delta and (Ba,Sr)(Co,Fe)O3 - delta, demonstrates the importance of ionic conductivity-i.e., high oxygen vacancy concentration as well as vacancy mobility-as a key factor for the surface oxygen exchange rate. This interpretation is corroborated by ab initio calculations, which indicate that the approach of an oxygen vacancy to oxygen intermediates adsorbed on the surface is the rate determining step for a number of perovskites.